1. Field of the Invention
The present invention relates to a method of forming a capacitor of a semiconductor device, and more particularly to a method of forming a capacitor of a semiconductor device, which enables the endurance of a capacitor to be secured while securing a desired charging capacitance.
2. Description of the Prior Art
Recently, as the high integration of a memory product is accelerated due to the development of semiconductor fabrication technique, a unit cell area is greatly reduced and an operation voltage is lowered. However, despite the reduction of cell area, it is still requested that the charging capacitance required for operating a memory device be sufficiently high and not less than 25 fF/cell to be sufficient for preventing the occurrence of a soft error and reduction of refresh time.
Accordingly, even though three-dimensional storage electrodes each having an electrode surface of a hemisphere shape have been applied to nitrogen-oxide (NO) capacitors for dynamic random access memories (DRAM's), which employ a Si3N4 film currently deposited as a dielectric using di-chloro-silane (DCS), the heights of the No capacitors are continuously increased so as to secure a sufficient capacitance.
As well known in the art, the charging capacitance of a capacitance is proportional to a surface area of an electrode and a dielectric constant of a dielectric material and reversely proportional to a space between the electrodes, i.e., the thickness of the dielectric.
Meanwhile, the NO capacitors reveal limitations in securing a charging capacitance required for a next generation DRAM of no less than 256 Mbit; accordingly, in order to secure a sufficient charging capacitance, the development of capacitors employing a dielectric film such as Al2O3 or HfO2 as a dielectric material is vigorously progressed.
However, an Al2O3 dielectric film has a limit in securing a charging capacitance because its dielectric constant (ε=9) is merely two times of that of SiO2 (ε=3.9) and is not so high. In addition, a HFO2 dielectric film and a LaO2 dielectric film have dielectric constants of about 20 and 27, respectively, and are more advantageous than the Al2O3 dielectric film from a standpoint of securing a charging capacitance; however, the leakage current is increased and the strength of breakdown voltage is greatly reduced if the equivalent oxidation film Tox thickness of a dielectric of a capacitor is reduced to about 15 Å, whereby the dielectric film contributes to the deterioration of endurance of the capacitor so that the capacitor is weaken by repeated electric impact.
Consequently, at present, each of the Al2O3, HfO2 and La2O3 films is substantially difficult to employ as a dielectric film capable of securing the endurance of a capacitor while securing a desired charging capacitance.